Application of the sequential t-test algorithm for analysing regime shifts to the southern Benguela ecosystem

Long-term, Ecosystem-Scale Changes in the Southern Benguela Marine Pelagic Social-Ecological System: Interaction of Natural and Human Drivers

“…These results were confirmed by Blamey et al (2012), who further refined the analyses of Howard et al (2007) and Roy et al (2007) to indicate increased variability of upwelling at the west coast since 1996 (a situation detrimental to sardine), and increased upwelling (i.e., productivity) at the south coast in the period 1996-2003, in line with increased availability and recruitment of small pelagics along the south coast.…”

“…Decadal-scale environmental regime shifts on the west coast were identified by Howard et al (2007), and Shannon et al (2010) for 1958-68 (increased sea surface temperature (SST)), 1971-81 (increased upwelling, i.e., an environmental regime detrimental to sardine and favoring anchovy), 1991-2001 (decreased upwelling and increasing SST off the northern part of the west coast, i.e., conditions more favorable for sardine recruitment) and in the early 2000s (further increasing SST/ reduced upwelling). These results were confirmed by Blamey et al (2012), who further refined the analyses of Howard et al (2007) and Roy et al (2007) to indicate increased variability of upwelling at the west coast since 1996 (a situation detrimental to sardine), and increased upwelling (i.e., productivity) at the south coast in the period 1996-2003, in line with increased availability and recruitment of small pelagics along the south coast.…”

“…Based on these findings, Howard et al (2007) postulated two regime shifts at the scale of the pelagic ecosystem, one in the early 1960s, following the collapse of the sardine population on the west coast (fishery-induced), and the other in the early 2000s, indicated by a shift in the relative abundance of small pelagics from the west coast to the south coast in a situation of very high population sizes of both species (likely environmentally-induced). Blamey et al (2012) added to these findings an ecosystem regime shift in the inshore in the first half of the 1990s, when the majority of the rock lobster catches moved from the west coast to the southwest coast, the spatial change impacting, through mechanisms related to predation and habitat provision, sea urchins and abalone as well as cormorants.…”

“…In addition to interannual variability, decadal-scale environmental conditions have been documented as favoring one species over another or both species simultaneously (van der Lingen et al 2006a, b). Recent research has focused on determining decadal-scale environmental (oceanographic) conditions and how and when they change (tipping points), as well as the impact of such changes at the scale of the entire ecosystem (Howard et al 2007, Blamey et al 2012. Decadal-scale variability is important for management purposes, because human activities in the ocean should be managed according to the prevailing regime in the ecosystem (e.g., King and McFarlane 2006).…”

Communicating changes in state of the southern Benguela ecosystem using trophic, model-derived indicators

“…In the second half of the 1990s, a shift in the relative distribution of small pelagic fish (anchovy and sardine) took place (van der Lingen et al 2002, Fairweather et al 2006, which lasted until the second half of the 2000s and is hypothesised to have been a result of changing environmental conditions (Howard et al 2007, Roy et al 2007, Blamey et al 2012. A smaller proportion than previously of small pelagic fish were distributed along the west coast and a larger proportion along the south coast during the period examined in this study (2004 to 2008).…”